Modern hearing assistance devices typically include digital electronics to enhance the wearer's experience. In the specific case of hearing aids, current designs employ digital signal processors rich in features. Their functionality is further benefited from communications, either from a remote source or from ear-to-ear for advanced processing. Thus, it is desirable to add wireless functionality to a hearing instrument to allow for functions such as ear-to-ear communications, wireless programming, wireless configuration, data logging, remote control, streaming audio, and bi-directional audio.
Frequencies available for use, such as the ISM frequencies at 900 MHz and 2.4 GHz, offer a large amount of bandwidth and allow sufficient RF power to cover many of the functions shown above. However these ISM frequencies are crowded with relatively high power interferers of various types. The radio in a hearing aid typically is a low power device that can run off of a very small low power battery. The challenge is to build a sensitive receiver with good linearity with minimal voltage and current. The radio and its support components typically are small and occupy as little volume as possible. Typically a radio transceiver in the 900 MHz band will require a frequency stable reference oscillator usually involving a quartz crystal as its resonating element. These devices are relatively large and need mechanical stability and special packaging.
What is needed in the art is a compact system for reliable, low power communications in a hearing assistance device. The system should be useable in environments with radio frequency interference.